Approval of Bristol-Myers Squibb’s (NYSE:BMY) Yervoy [ipilimumab] for melanoma in March 2011 marked the second victory for the field of active immunotherapy in oncology within a year, with the first being the U.S. Food and Drug Administration [FDA] approval of Dendreon Corporation’s (NASDAQ:DNDN) Provenge [sipuleucel-T] for metastatic castrate-resistant prostate cancer [CRPC] in April 2010. Ipilimumab and sipuleucel-T were the first two active immunotherapies for cancer to demonstrate improved survival in randomized Phase 3 trials and both were published in the prestigious New England Journal of Medicine within one month of each other.
The similarities don’t end there, as both ipilimumab and sipuleucel-T have reignited enthusiasm for the field of active immunotherapy. Accordingly, the purpose of this article is to highlight some of the other parallels between these two innovative agents.
Both Studied in Prostate Cancer
While ipilimumab was recently approved for the treatment of melanoma, the product has also been extensively studied in prostate cancer. In fact, there are eight clinical studies with ipilimumab in prostate cancer according to ClinicalTrials.gov, including five that are currently active or recruiting.
One particular prostate cancer study made headlines in June 2009 when investigators at the Mayo Clinic reported in the online research magazine Discovery’s Edge that the combination of a single dose of ipilimumab [3 mg/kg] with androgen ablation therapy dramatically reduced the tumor size in two patients, making surgery possible for both patients whose prostate cancer had been previously considered inoperable. The controversial results from a handful of patients were met with skepticism and the complete Phase 2 results with 108 patients with advanced prostate cancer were later reported at the American Society of Clinical Oncology [ASCO] 2010 Genitourinary Cancers Symposium [abstract #168]. According to the ASCO abstract, patients treated with androgen ablation either alone or in combination with ipilimumab demonstrated a greater than 97% decline in testosterone levels, underscoring the possibility that the tumor reductions in a few patients could have been associated with androgen ablation. Patients treated with ipilimumab, however, were more likely to have undetectable prostate specific antigen [PSA] by three months [55% vs. 38%].
A Phase 3 trial with ipilimumab following radiation therapy in patients with CRPC that have received prior treatment with docetaxel is ongoing [ClinicalTrials.gov identifier NCT00861614].
Two Is Better than One
As the first two active immunotherapies approved for the treatment of cancer, it wouldn’t be surprising to see the products studied in combination in prostate cancer – especially in view of the fact that ipilimumab has already been studied in this disease. Sipuleucel-T may help build an effective immune response to kill tumor cells, while ipilimumab may stimulate the immune system through T-cell activation and proliferation and stop tumor cells from growing. Accordingly, giving vaccine therapy together with ipilimumab may be an effective treatment for prostate cancer. Interestingly, the only such combination study listed on ClinicalTrials.gov relates to a completed Phase 1 trial with ipilimumab in combination with Bavarian Nordic’s Prostvac, an "off-the-shelf" therapeutic cancer vaccine moving into pivotal Phase 3 clinical development [ClinicalTrials.gov identifier NCT00124670].
Both Dendreon’s sipuleucel-T and Bristol-Myers’ ipilimumab have been criticized as overly expensive new therapies.
The cost of sipuleucel-T is approximately $93,000 for a course of treatment, which consists of three infusions at two-week intervals. In view of the fact that the product has been demonstrated to extend median survival by 4.1 months, this translates into an average cost of $23,000 per month of added survival.
In comparison, Taxotere [docetaxel] by Sanofi-aventis (NYSE:SNY) is indicated for the treatment of CRPC and is administered every 3 weeks for 10 cycles. Assuming an average monthly cost of $4,000 for docetaxel [source: Cancer Res 2009;69(24 Suppl):Abstract nr 1076], this is an approximate total cost of $40,000 per patient. In the pivotal TAX 327 study, median survival for prostate cancer patients receiving docetaxel was 18.9 months versus 16.5 months in the control arm, which results in an average cost of $16,666 per month of added survival or about 28% less than sipuleucel-T. Updated survival analysis of the TAX 327 study demonstrates a 2.9-month survival advantage, which lowers the average cost to $13,793 per month of added survival or about 40% less than sipuleucel-T. Unlike sipuleucel-T, however, treating common adverse reactions with docetaxel, such as infections, neutropenia, anemia, nausea, diarrhea, and others, increases the total cost of therapy – and more importantly negatively impacts the patient’s quality of life. As such, the pricing of sipuleucel-T doesn’t appear completely out of line.
According to the prescribing information, ipilimumab is administered intravenously [3 mg/kg] over 90 minutes every 3 weeks for a total of four doses. Bristol-Myers is pricing each dose at $30,000, which translates into a total cost of $120,000 for a full course of therapy. In the pivotal ‘020 study, median survival for melanoma patients receiving ipilimumab was 10.1 months versus 6.4 months in the control arm. The average cost per month of added survival is approximately $32,432, which is 41% higher than the only other active immunotherapy for cancer, sipuleucel-T.
However, on March 21, 2011, Bristol-Myers announced that the ‘024 study [ClinicalTrials.gov identifier NCT00324155] met its primary endpoint of overall survival. Minimal details were provided, but an abstract of the ‘024 data is expected to be submitted to ASCO for potential presentation at the Annual Meeting in June 2011. The ‘024 study is in patients with untreated Stage III [unresectable] or IV melanoma receiving dacarbazine plus 10 mg/kg ipilimumab versus dacarbazine with placebo. If the median survival for patients in the ipilimumab arm is 5.2 months or greater than the placebo arm [versus 3.7 month difference in the ‘020 study], then the pricing of ipilimumab per month of added survival would be comparable to sipuleucel-T.
Prostate and Melanoma Highly Competitive
Melanoma and prostate cancer are the two most crowded clinical development segments within the active immunotherapy field. As such, both ipilimumab and sipuleucel-T may face competition from other active immunotherapies in the near future. In addition, the products may soon encounter small molecule rivals.
For example, Johnson & Johnson’s (NYSE:JNJ) abiraterone acetate significantly improved overall survival for patients with metastatic advanced prostate cancer. Based on the positive Phase 3 results, the company has filed marketing applications for abiraterone acetate with regulatory authorities worldwide for the treatment of metastatic advanced prostate cancer that has developed resistance to conventional hormonal therapies. Not far behind, Medivation, Inc. (NASDAQ:MDVN) is evaluating its MDV3100 product candidate in collaboration with Astellas Pharma, Inc. (OTCPK:ALPMY). The Phase 3 AFFIRM trial with MDV3100 has completed enrollment of men with advanced prostate cancer who were previously treated with docetaxel-based chemotherapy and the Phase 3 PREVAIL trial with MDV3100 is currently enrolling men who have not yet received chemotherapy
In addition, Plexxikon, Inc. [being acquired by Daiichi Sankyo Company, Limited (OTC:DSKYY)] and co-development partner Roche Holding (OTCQX:RHHBY) are advancing PLX4032, an oral drug candidate that targets the oncogenic BRAF mutation present in about half of melanoma cancers and about eight percent of all solid tumors. Interim data from a Phase 3 controlled study of PLX4032 in previously untreated metastatic melanoma patients with the BRAF mutation met both co-primary endpoints. Patients treated with PLX4032 had improved overall survival and improved progression-free survival compared to patients treated with dacarbazine, the current standard of care. A New Drug Application [NDA] for PLX4032 is expected in 2011.
Some new agents might actually be synergistic with active immunotherapies instead of representing potential competition. This was a central theme at the recent Cancer Immunotherapy Consortium’s 2011 Scientific Colloquium titled "Schedule and Dose for Combination Therapy."
Both ipilimumab and sipuleucel-T represent important clinical advances for the field of active immunotherapy in oncology and for patients with melanoma and prostate cancer, respectively. Further, with nearly 50 clinical programs currently underway, including nearly a dozen that are in pivotal Phase 3 development, we expect to see five active cancer immunotherapies approved by 2015. Beyond these clinical accomplishments, however, industry observers will be closely monitoring the commercial success of these innovative agents in view of the product pricing, supply constraints, and competitive dynamics identified to date.
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